The magnitude of voltage required to breakdown a spark plug gap depends on many factors including electrode material, electrode shape, gap distance, temperature, chemical composition of the gas in the gap, pressure, and ion concentration in the gap. The durability testing of ignition coils is typically performed by using brass needle point gaps in air at atmospheric pressure. The breakdown voltage to be tested is implemented by varying the gap between the needle points. Once breakdown voltage is achieved, then a sustaining voltage appears across the gap. The needle point gaps work reasonably well on breakdown voltages of up to 15 kilovolts. However, testing above 15 kilovolts with needle point gaps provides a breakdown voltage which may vary as much as plus or minus 5 kilovolts when testing for 25 kilovolts.